Polarization dependence of absorption and luminescence spectra on each crystal face of α‐bithiophene and α‐terthiophene

Polarization dependence of the absorption spectra and the luminescence spectra in α-bithiophene and α -terthiophene has been measured directly with near normal incident light on the ab, bc, and ca crystal planes of their thick single crystals. The absorption spectra were obtained from the reflection spectra using the Kramers-Kronig transformation. Vibronic excitons (Frenkel excitons) have been observed on each crystal plane of α-bithiophene and α-terthiophene. The polarizations of the absorption spectra are consistent with the prediction obtained from the MOPAC calculations of the transition dipole moment directions of the molecules in the single crystals.